Internal combustion engine systems such as Diesel engines use exhaust-gas recirculation components to return a portion of the combustion gases of the internal combustion engine to a fresh-air supply of the internal combustion engine, in order to resupply this portion of the combustion waste gas together with fresh air to the internal combustion engine. In internal combustion engine systems, especially Diesel engines, that are equipped with an exhaust-gas turbocharger, it is distinguished between high-pressure exhaust-gas recirculation and low-pressure exhaust-gas recirculation. The high-pressure exhaust-gas recirculation component connects a reservoir downstream from an exhaust-gas turbine of the exhaust-gas turbocharger to an intake manifold of the internal combustion engine via a high-pressure exhaust-gas recirculation valve. The low-pressure exhaust-gas recirculation component connects an output of the exhaust gas system of the internal combustion engine, e.g., downstream from a particle filter, to a fresh-air supply upstream from a compressor of the exhaust-gas turbocharger. To achieve more precise control of the exhaust-gas recirculation, it is of great importance to obtain the most precise knowledge of the flow characteristics of the exhaust-gas recirculation component and the pressure conditions within the exhaust-gas recirculation component.
In this context, a method for operating an electronically controlled internal combustion engine is described in U.S. Pat. No. 7,474,954, in which a differential pressure sensor of a high-pressure exhaust-gas recirculation component is calibrated automatically. For this purpose an output of the differential pressure sensor is monitored when the engine is switched off, an actual deviation is determined and, if appropriate, a corresponding offset value is stored in a non-volatile manner.
U.S. Patent Application Publication No. 2008/0295514 relates to a control method for an internal combustion engine having a high-pressure exhaust-gas recirculation component and a low-pressure exhaust-gas recirculation component, in which an exhaust-gas recirculation quantity is adjusted such that a temperature of an exhaust-gas catalyst lies within a target range. To learn an opening amount of a high-pressure exhaust-gas recirculation valve and a low-pressure exhaust-gas recirculation valve, it is ascertained whether a fuel supply is switched off or whether the internal combustion engine is idling. A learning cycle is implemented as a function of this determination, in which the low-pressure exhaust-gas recirculation valve and the high-pressure exhaust-gas recirculation valve are closed completely and are then fully opened in predefined steps.
European Published Patent Application No. 1 870 584 relates to an exhaust-gas recirculation device of an internal combustion engine having an exhaust-gas turbocharger, a low-pressure exhaust-gas recirculation component and a high-pressure exhaust-gas recirculation component. According to one specific arrangement, an air supply quantity and the exhaust-gas recirculation rate are set to reference values and the relation between the low-pressure exhaust-gas recirculation gas quantity flowing through the low-pressure exhaust-gas recirculation component, and an opening degree of devices that are able to set the exhaust-gas recirculation gas quantity is learned and corrected, based on a differential pressure above a valve recorded by a differential pressure sensor.
Finally, PCT International Published Patent Application No. WO 2009/037543 describes an exhaust-gas recirculation device for an internal combustion engine, which has a high-pressure exhaust-gas recirculation component and a low-pressure exhaust-gas recirculation component. The high-pressure exhaust-gas recirculation component is controlled such that an oxygen concentration of the air aspirated into the cylinders corresponds to a target value that is set according to the operating state of the internal combustion engine. The low-pressure exhaust-gas recirculation component is controlled such that the low-pressure exhaust-gas recirculation gas is conducted into the intake at a target flow rate.
The low-pressure exhaust-gas recirculation component is undergoing continuous further development, one focus in the development being a reduction of flow losses through the low-pressure exhaust-gas recirculation circuit. However, in systems which are optimized with regard to flow losses there are problems with the overall system regarding the robustness of the metering of the low-pressure exhaust-gas recirculation gas. For example, if such a system is operated on an engine test stand or a chassis dynometer, such as for certification purposes, the exhaust-gas measuring technology creates interference. Due to the aspiration or thinning of the exhaust-gas, a different vacuum pressure than would be the case in a standstill of the vehicle is produced at the end of the exhaust gas system. This vacuum pressure may even cause fresh air from an intake region downstream from the compressor to reach the exhaust gas system directly through the low-pressure exhaust-gas recirculation component. All in all, a system that is optimized with regard to flow losses responds to pressure changes at the end of the exhaust gas system in a sensitive manner. Even a slight fault in the exhaust-gas pressure such as 10 hPa, for instance, interferes considerably with the low-pressure exhaust-gas recirculation component, since such a fault is of a similar order of magnitude as the required scavenging gradient of the low-pressure exhaust-gas recirculation component. Detecting the pressure at the output of the exhaust gas system with the aid of a pressure sensor is technically difficult, since the sensor preferably would have to have an accuracy of less than 1 hPa at a burst pressure of 1000 hPa, for instance, and furthermore, would have to be usable in the technically difficult environment of the exhaust gas system.